Auxiliary discharge gas amplifier and the like



Jan. 16, 1962 E. o. JOHNSQN AUXILIARY DISCHARGE GAS AMPLIFIER AND THE LIKE Original Filed Sept. 20, 1950 3 Sheets-Sheet 1 INVENTOR. EDWF-IRD El. .Jnmvsum F W/Z L Jan. 16, 1962 E. o. JOHNSON 3,017,533

AUXILIARY DISCHARGE GAS AMPLIFIER AND THE LIKE Original Filed Sept. 20, 1950 3 Sheets-Sheet 2 INVENTOR. EDWHRD D- .JuHNsuN Jan. 16, 1962 E. o. JOHNSON 3,017,533

AUXILIARY DISCHARGE GAS AMPLIFIER AND THE LIKE Original Filed Sept. 20. 1950 '3 Sheets-Sheet 8 4 INVENTOR.

'' b EDWHRD U. JOHNSON United States Patent 3,017,533 AUXILEARY DESCHARGE GAS AMPLIFIER AND THE LIKE Edward 0. Johnson, Princeton, N.J., assignor to Radio Corporation of America, a corporation of Delaware Continuation of abandoned application Ser. No. 185,745,

Sept. 20, 1950. This application May 8, 1956, Ser.

27 Claims. (Cl. 313-189) This application is a continuation of my copending application Serial No. 185,745, filed September 20, 1950, now abandoned.

My present invention relates to electron discharge devices of the class in which an ionizable medium is used to support a discharge. More particularly my invention relates to such a device in which an electrode may continuously control or modulate the current through the device as well as to a system and method for operating the same.

It has long been the object of continuing research and experiment to provide a gas discharge device embodying the more desirable characteristics of vacuum tubes and at the same time be able to pass the relatively large currents characteristic of gas tubes.

It has been desired to effect this while at the same time eliminating certain of the less desirable gas tube characteristics, examples of which will be pointed out. One feature of vacuum tubes which has been the object of considerable effort to build into gas tubes is that of continuous grid control over the current flowing through the tube. This continuous grid control should operate through a range from cut-cit to a maximum useful output measured in amperes. -As will be pointed out some success has been attained in achieving this. However, the resulting gas discharge devices, except for one or two exceptions with which I am familiar, differ from the usual gas tubes in that they are relatively high impedance devices and operate at voltages which are high as compared to the ionization potential of the gas employed. Furthermore, such devices difier from my invention in that the less desirable gas tube characteristics are still present therein. It may be well at this point for a better understanding of my invention to discuss one type of gas tube, the so-called thyratron, employing a cathode, grid and anode and having a relatively low impedance as compared to vacuum tubes. In a thyratron, the bias on the grid holds 01f an applied anode potential until the signal applied to the grid makes it sufiiciently less negative to permit breakdown and the consequent formation of a self-sustaining discharge. As is well known in the art, such breakdown is caused by electrons from the cathode colliding with the atoms of the gas in the load current path between the cathode and the anode with suificient energy to ionize the gas and thereby render it conductive. During the discharge, except for the sheath regions very close to the cathode and the anode, the load current path between the cathode and the anode in a gas discharged device is filled with a conductive plasma made up of a dense concentration of negative electrons and positive ions. In the case of the thyratron, during discharge, the grid is surrounded by a sheath of positive ions, assuming the case of a grid negative to the cathode, and the field of the grid does not extend into the plasma. The plasma is generally understood as having densities of positive and negative particles, i.e., ions and electrons, which are equivalent or substantially equal, and extends continuously through the space between the cathode and anode sheaths.

As is known, after breakdown occurs in a thyratron, it is impossible to render the device non-conductive by making the grid more negative. Thus, the thyratron type of tube is an on-oif device and the current flowing through the device cannot be controlled by variations in grid potential. A sudden change in grid potential to render it more negative acts momentarily to increase the thickness of the grid sheath and more narrowly constrict the grid openings. However, the effect of this is to increase the potential drop or field intensity through the grid openings with a resultant speeding up of the electrons flowing therethrough under the influence of the field from the anode. The increased electron velocities cause increased ionization which in turn acts to reduce the thickness of the grid sheath. Thus, changes in grid potential to render the same more negative only affect the average sheath thickness to a small extent without producing any appreciable variation in anode current.

The voltage drop across a gas tube after the formation of a discharge has an average value as measured by a direct current meter approximately equal to the ionizing potential of the gas in the tube and varies in accordance with the electrode spacings and other physical character istics. However, the dynamic picture presented is entirely different. When breakdown occurs and a discharge forms there is an instantaneous drop in the voltage across the tube below the ionization potential of the gas and ionization ceases. However, residual plasma suflices to neutralize space charge and serves as a conducting path for the characteristically large currents for some time. The residual plasma gradually becomes depleted or decays during this interval of time while at the same time the voltage across the tube increases to a point where it is once again slightly greater than the ionization potential of the gas (although lower than the voltage drop across the tube prior to breakdown as in a thyratron). This phenomena sets up oscillations in the plasma of gas tubes which render them unsuitable for a wide variety of applications.

In general, gas tubes have a relatively low upper frequency at which they may be operated because of the time required for deionization or recapturing control. This results from the relatively slow speed of the ionsas compared to the electrons. This aspect of gas tubes and in particular thyratrons is discussed in detail in the copending application of L. Malter, Serial No. 148,976, filed March 10, 1950, now US. Patent No. 2,662,993, and assigned to the assignee of the present application. It is believed suflicient to point out here that the rate at which the plasma decays depends to a large extent on the mobility of the relatively massive and slow moving positive ions. The plasma in a tube forms a highly conductive path having negligible impedance. Just as the conductivity of a copper wire depends upon its cross section thickness, the conductivity of the plasma is proportional to its density. As in the case of a decaying plasma, the rate at which the density or conductivity of the plasma may be varied or modulated has an upper limit which is determined in part by the mobility or diffusion time of the relatively slow moving positive ions. Thus, in a thyratron, a finite time known as the deionization time or recovery time, must elapse after removal of the anode potential before the anode potential may be reapplied. If the anode potential is reapplied before sufficient time has elapsed, the grid cannot prevent the tube from firing and it fires even though the grid is connected to its normal bias potential source. As will be pointed out, in accordance with my invention the current and voltage across a gas tube may be modulated at very high frewell known vacuum tubes may be operated at relatively high frequencies and the current passed may readily be continuously controlled by a grid or control electrode. Vacuum tubes contain few or appreciably no ions. As a result they are generally stable and are not subjected to the plasma oscillations characteristic of gas tubes.

The usual gas tube, as has been pointed out, has a relatively low impedance as a consequence of space charge neutralization, among other things, by the positive ions. Vacuum tubes on the other hand have a relatively high impedance. One approach to the problem of building continuous current control by a control electrode into a gas tube was to avoid the presence of suflicient ions to support a discharge in the grid-anode region or in the vicinity of the control grid. Such devices in effect provided a virtual cathode in the form of the plasma quite close to the grid. However, the grid or grid region represented a rather high impedance requiring comparatively high anode potentials to secure conduction. The absence of ions in the grid region resulted in a dark space around the grid, i.e., the absence of a visible discharge or glow. Devices of this class, that is where the grid and anode are closely spaced or where the grid is surrounded by a dark space, though making possible grid control, are not free from the less desirable characteristics of gas tubes such as noise resulting from oscillations in the plasma being present at least in the cathode region. Nor do such tubes have the often desirable low impedance characteristic of gas tubes.

It has also been proposed to provide a tube which operated with two distinct plasma regions separated by a control electrode or grid. In this type of device an ionizing discharge occurs in the grid cathode region between the legs of a single filament or between two separate filaments. The plasma in the grid cathode region or cathode plasma does not extend through the grid but acts as. a source of electrons which may pass through the grid. In view of the relatively large grid-anode spacing and potential difference, the electrons which pass through the grid create additional ionization as they approach the anode. The additional ionization results in a plasma in the grid-anode region. This type of tube also requires a relatively high anode potential and therefore has a relatively high impedance and may be noisy as a result of the plasma oscil lations.

Still another class of tubes described in the literature may be broadly referred to as tubes having a cathanode in which a secondary glow appears between the grid and anode. Again relatively high anode potentials are utilized and the grid itself is surrounded by a dark space. In such devices the grid also represents a high impedance across the tube between cathode and anode. Such tubes have the limitations previously discussed.

The ability of positive ions to overcome the space charge effect is well known. It has been suggested that an auxiliary ionizing discharge in a gas rectifier may be economically utilized to create a plasma to pass the current between the main cathode and anode. In this instance, the main anode potential may be materially less than that of the ionization potential of the gas.

However, I believe that heretofore it has not been known or understood that a control electrode immersed in the plasma extending continuously from close to the cathode to close to the anode and through the grid may under certain conditions exercise continuous control over the current passing through the device as in a vacuum tube. As will be made clear, such an electrode may be used to modulate large currents at very high frequencies.

It is, therefore, a pricipal object of my invention to provide a gas discharge device having a smooth voltampere current characteristic similar to that of a vacuum tube, and which is highly stable and free from distortion in operation and in which the current may be continuously modulated at radio frequencies.

Another object is the provision of a gas discharge device in which a control electrode may be used to continuously control the flow of curent therethrough and in which the plasma oscillations do not distort the output.

Another object is the provision of such a device which has an extremely low impedance and a tube drop of approximately one or two volts.

Yet another object is the provision of a gas discharge device in which the ionization required to reduce the space charge effect is created independently of the potential of the anode, and in which the plasma created extends between the cathode and anode and through the control electrode.

Still another object is the provision of a gas discharge device in which a control electrode is immersed in the plasma formed in the device and retains control over the current passing therethrough.

A more specific object is the provision of a gas discharge device in which an ionizing discharge is formed along a path which is mainly outside of the main or useful current path.

Another more specific object is the provision of a gas discharge device in which an ionizing or auxiliary discharge is formed to create a plasma which serves to conduct the main current, the control grid being designed so as not normally to interfere materially with the creation of plasma.

Further objects and advantages will become evident as my invention is more fully understood.

In the embodiments exemplifying my invention, I provide for the formation of a continuous conductive plasma in a gas triode which normally extends between the main cathode and anode without interruption independent of the potentials applied to the main current path. The plasma extends through the grid or control electrode. I also preferably utilize a focused stream of electrons formed from an ionizing or auxiliary cathode to create the plasma which serves to form a highly conductive path between the main cathode and anode and through the control electrode.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. The invention itself will be best understood by reference to the following description taken in connection with the accompanying drawing in which:

FIGURE 1 is a sectional view through the line 11 of FIGURE 2 of a gas discharge device constructed in accordance with my invention;

FIGURE 2 is a sectional view through the line 22 of FIGURE 1;

FIGURES 3, 4 and 5 are transverse sectional views of gas discharge devices partially schematic and illustrative of means for carrying out certain features of my inventron;

FIGURE 6 is a transverse sectional view of still another form of double auxiliary discharge device;

FIGURE 7 is a sectional view through the line 7-7 of FIGURE 6;

FIGURE 8 is a transverse sectional view of a gas discharge mixer tube embodying certain features of my invention;

FIGURE 9 is a sectional view through the line 99 of FIGURE 8; and

FIGURE 10 is a view showing volt-ampere current characteristic curves of the device shown in FIGURE 1.

As pointed out above, a grid or control electrode across the ionizing current path, as in the case of the grid in a thyratron, appears to be opposed by the plasma. When the grid is made more negative, the constrictions formed result in more intense ionization which offsets the effect thereof. In fact, as pointed out, the net effect on the current which sustains the plasma of driving the grid more negative is negligible.

I have found that a control electrode or grid immersed in plasma can continuously control a current, which for Convenience will be labled the main current, so long as the current which sustains the plasma is not affected by the grid potential excursions. This latter current will be called the ionization or auxiliary current. The full main current may flow with as little as one or two volts while a sufficiently high voltage is across the ionization or auxiliary current path as will cause ionization. I have demonstrated that with such an arrangement, i.e. one in which the plasma normally extends substantially between the end electrodes of the load current path and through a control electrode, the control electrode can be utilized to modulate the main current at very high frequencies. I have found that when the plasma is thus sustained by a current which is not affected by the potential swings of the control electrode or grid, the sheath around this electrode will increase and decrease the thickness as the electrode potential is increased and decreased. I believe that since the ionization or auxiliary current is not affected, the grid sheath can constrict and completely close the grid openings to the flow of current without the plasma tending to oppose the formation of these constrictions. This is the case even though normally, that is when the grid permits the load current to flow to the anode, the plasma extends through the openings of the control electrode without any discontinuity appearing at the openings and with the plasma on each side of the control electrode joined through the openings in one continuous mass.

Devices constructed in accordance with my invention readily lend themselves to many diversified uses and as will be apparent specific constructions may be varied to best adapt the device for specific uses.

Referring now to the drawings and FIGURES l and 2, in particular, gas discharge device is illustrative of one more preferred form which my invention may take and comprises a gas-tight envelope 11 only partially indicated in FIGURE 1. The device is provided with the usual stem 12 through which the lead-in conductors may be sealed as indicated. A thermionic unipotential oxide coated cathode is supported between upper and lower insulating supports such as micas 14, 15. A U-shaped control grid 16 and U-shaped anode 17 are also supported between micas 14, and as shown partially enclose cathode 13. Grid 16 comprises a pair of U- shaped support members 18, 19 between which a plurality of parallel grid wires 20 are supported in spaced relation. As will be more fully pointed out grid wires 20 are comparatively widely spaced apart and as will be seen do not normally materially interfere with the diffusion of the plasma therebetween. Grid 16 is provided with support members 21 which extend through micas 14, 15 and serve to rigidly mount the grid. Anode 17 is made of sheet metal and has connected thereto support rods 22 which serve to rigidly lock the anode between upper and lower micas 14, 15. Opposite the open ends of grid 16 and anode 17 is mounted a cylindrical focusing electrode 23 supported in a similar manner between micas 14, 15 by means of support rods 24 connected thereto by means of welding or the like. An ionization or auxiliary cathode 25 is mounted coaxially and concentric with respect to cylindrical focusing electrode 23. Auxiliary cathode 25 is preferably, as indicated in FIGURE 1, a thermionic oxide coated unipotential cathode similar to main cathode 13.

Both main cathode 13 and auxiliary cathode 25 have a conventional nickel sleeve Within which non-inductive type heaters 27, 28 extend.

As shown in FIGURES l and 2 focusing electrode 23 is provided with an elongated narrow slot 26, the center of which extends along a plane passing through the axes of auxiliary and main cathodes 25 and 13. By providing focusing means in the form of electrode 23, around auxiliary cathode 25, having a narrow slot 26. I have found that the desired degree of ionization may be attained with a considerable reduction in the expended power as com- 6 pared to a similar device without such a focusing electrode.

As shown in FIGURE 1, one of the grid support members 21 is connected to a lead-in conductor 29 which is sealed through stem 12. One of the anode support rods 22 is connected to a supporting conductor 30, while one of the focusing electrode support rods 24 is connected to a supporting conductor 31. Both supporting conductors 30, 31 are sealed through stem 12 and serve as the main support members between stem 12 and the electrode assembly. Lead-ins 32 and 33 are connected to the leads of heater 27 while, as shown, the lead-in 32 is connected to the sleeve of cathode 13. Similarly, auxiliary cathode 25 is connected to lead-in 34 while the leads of heater 28 are connected, respectively, to lead-ins 34 and 35.

Gas discharge device 10 is processed in the well known manner and as well known in the art is provided with a gaseous atmosphere prior to scaling off. Any suitable gas or mixture of gases may be utilized. The gas pressure will vary in accordance with the specific envelope and electrode geometry and spacings. Furthermore, I do not believe the gas pressure to be critical except that I preferably utilize a pressure which will favor the formation of a self-sustaining ionizing discharge. In the tube now being described as being illustrative of my invention and which has been shown for convenience on an enlarged scale of approximately two to one, I have used helium at.

a pressure of approximately 750 microns though other gases and other pressures may be used.

I believe that an important feature of my invention resides in the fact that the spacings between adjacent grid wires 20 is large compared to the mean free path of a positive ion in the gas. In the particular tube being described, the grid wire spacing is also large as compared to the mean free path of the electrons in the gas. In practice the gas pressure may vary from approximately microns to several millimeters of mercury. In operating gas discharge device 10, I normally connect auxiliary electrode 25 and focusing electrode 23 together and connect them to the negative side of a source of potential 36 through a current limiting resistance 37. I connect main cathode 13 to the positive side of potential source 36. Anode 17 and main cathode 13 are connected across a source of potential 38 with the anode connected to the positive side through a load impedance as shown. Control grid 16 is connected to the negative side of a source of biasing potential 39. The sources of potential have been indicated as simple batteries but it is, of course, understood that any suitable sources may be utilized. The potentials are so selected or adjusted that between auxiliary cathode 25 and main cathode 13 a potential difference exists which is sufficient to cause an ionizing discharge to appear therebetween. The potential difference between auxiliary and main cathodes 25 and 13 may be approximately 40 volts. Between the main cathode and anode 17 I impress a potential difference which may vary from approximately zero to twenty-five volts while the grid bias may vary from approximately one or two volts positive to approximately twenty volts negative with respect to the main cathode.

In operation in a circuit as described and as shown in FIGURE 1, device 10 has an anode volt-ampere current characteristic as illustrated by the curves of FIGURE 10. In these curves I is the main anode current in milliamperes. E is the main anode potential in volts. E is the grid potential in volts. With zero grid voltage the full main current flows with the main anode at a potential of approximately one to two volts. It is apparent that as the grid swings about its bias potential the main current is controlled over a wide range of approximately 0200 or more milliamperes. The main current is effectively cut off with approximately 20 volts on the grid.

When the tube is operating, an intense visible discharge extends outwardly from slot 26 and bathes main cathode 13. It is apparent that focusing electrode 23 acts to focus the electron stream from auxiliary cathode 25. Furthermore, electrode 23 acts to intensify the ionization and thereby make it possible to secure the desired plasma density with an exceedingly small amount of current or power being expended in the ionization or auxiliary circuit. In fact, only approximately S15 milliamperes need be used in the auxiliary circuit while in securing the data for the curves shown in FIGURE 10, the ionization or auxiliary current was only milliamperes. In the present case, main cathode 13 acts as the anode for the auxiliary cathode. For all practical purposes the auxiliary current collected by the main anode 17 is of negligible effect on the operation of the device. Instead of the ionization merely occurring in the close vicinity of the main cathode as may be the case in the absence of focusing electrode 2.3, ionization takes place substantially all the way from slot 26 to main cathode 13 in a highly intense manner. The plasma extends through the grid openings and in the grid-anode region as Well. Thus, there is a highly conductive path from the main cathode through the grid to the main anode except when the main current is cut-off by the grid.

When the grid potential is modulated by the incoming signal the effect on the plasma extending through the grid openings is instantaneous and at low frequencies may be visually observed. Gas discharge device It) has been readily operated at a frequency of fifteen megacycles or more with grid wires 2t) spaced approximately 2 mm. from anode 17. In the case of the on-off or thyratron type of operation, this frequency corresponds to a recovery time of approximately .03 microseconds. Conventional thymtrons can be turned off and on only at frequencies which correspond to at least ten microseconds. Hydrogen thyratrons are somewhat faster than this.

As pointed out above, the plasma formed in a gas dis charge is continuously decaying and requires sustaining. Thus, when the control electrode or grid 16 swings negative far enough to cut off the plasma in the grid-anode region of device 10, the grid-anode region is momentarily cut off from the plasma in the grid-cathode region. This tends to reduce the maximum frequency at which device It! may be operated since as the frequency is increased the diffusion time of the plasma through the grid to the anode becomes equivalent to and then large as compared to the time interval required for a grid cycle. One way in which the frequency at which device 10 may be operated can be increased is by reduction of the grid-anode spacing.

As apparent from FIGURE 1, anode 17 is spaced from focusing electrode 23 as indicated at 40'. If desired this space may be closed by suitable insulation. However, I have found that it is sufiicient to keep space 40 small as compared to the mean free paths in the gas. This effectively limits or prevents diffusion of plasma through space 4i) and an are around the exterior surfaces of the electrodes is prevented. As shown in FIGURE 1, the grid 16 and the focusing electrode 23 cooperate to isolate the main cathode from the anode 17 except for the apertures through the grid, thus effectively limiting the plasma and the main current to passing through the grid.

Devices constructed in accordance with my invention lend themselves to a great variety of uses. In many instances the resulting arrangement is better in operation even though much simpler and less costly. For example, in driving the voice coil of a loud-speaker in communication networks, it is customary to use a vacuum tube requiring a source of relatively high voltage and a costly transformer. When gas discharge device It) is utilized in place of the vacuum tube, lower voltages are used and the transformer is dispensed with entirely since device 10 is of such a low output impedance that when it is connected directly to the voice coil of the loudspeaker it delivers sufficient power to efficiently drive the same.

In FIGURE 3, I have shown schematically another arrangement for carrying out certain features of my invention. Gas discharge device 41 comprises a thermionic 8 z cathode 42, a grid 43 and an anode 44 in the order shown. A focusing electrode 45 and an ionization or auxiliary cathode 46 are mounted in or facing into the region between grid 43 and anode 4-4. In this case, source 36 is connected with its negative terminal connected to auxiliany cathode 46 and focusing electrode 45 and its positiveterminal connected to anode 44. Thus, anode 44 serves as the anode for both the ionization or auxiliary current and the main current. The grid 43 is'arranged to isolate the cathode 42 from the anode 44 except for the apertures through the grid, thus effectively limiting the plasma and the main current to passing through the grid. The plasma created in the grid-anode region diffuses through the grid into the grid-cathode region. As in the case of grid 16, grid 43 is constructed so that it does not normally materially impede the diffusion of plasma.

Both devices If and 41 have upper frequency limits which depend upon the diffusion time of the plasma as indicated in connection with device If). I further im prove the frequency response by providing means for sustaining the plasma in both the grid-anode and grid-cathode regions. In FIGURES 4, 5, 6 and 7 are shown devices in which the plasma on both sides of the control electrode or grid is sustained independently of diffusion through the grid. This serves to avoid the necessity of plasma diffusing through the grid to render the device conductive when the grid is modulated at such a high frequency rate that the time for diffusion through the grid to the anode is large compared to the peak-to-peak time interval for each grid excursion.

In FIGURE 4, gas discharge device 52 is similar to device 41 except that focusing electrode 47 is provided with two slots 48, 49. Slot 48 opens into the grid-anode region while slot 49 opens into the grid-cathode region. Adjacent the end of grid 43 opposite focusing electrode 47 and auxiliary cathode 5% is mounted an ionization or auxiliary anode 51 which functions as the collector for auxiliary cathode St The focusing electrode 47, and the anode 51 are arranged to isolate the main cathode 42 from the main anode 44 except for the openings through the grid 43. In operating such a device a source, such as source 36 of FIG. 1, is connected between auxiliary cathode 5t and focusing electrode 47 on the one hand and auxiliary anode 51 on the other. The circuit connections between main cathode 42, control grid 43 and anode 44 are the same as previously indicated for the corresponding electrodes in device 10. In the case of device 52, I preferably tie auxiliary anode 51 to main cathode 42 in such manner that they operate at substantially the same potential. With auxiliary cathode St) at a potential of approximately 40 volts negative to auxiliary anode 51 a visible discharge appears across device 52 from slot 48 to auxiliary anode 51 and from slot 49 to auxiliary anode 51. With a potential source of ap proximately 25 volts such as source 38 (FIGURE 1) having its negative terminal connected to main cathode 42 and its positive terminal connected to main anode 44, a very high frequency signal may be impressed upon control electrode or grid 43 to sufficiently modulate the current flowing between main cathode 42 and main anode 44. Since the plasma in both the grid-anode and gridcathode regions is being sustained independently of the rate of diffusion of plasma through the openings in grid 43, such a device may be operated at a frequency of approximately megacycles or more. During the period when the tube is conducting the plasma extends through the grid openings. During the negative swing of the grid, the grid sheath closes the grid openings and there is substantially no diffusion of plasma therethrough. In this device when the grid swings more positive the plasma need diffuse through only a relatively small area to re-es'tablish the continuous plasma which normally exists between main cathode and anode during conduction. In FIGURE 5, gas discharge device 55 is provided with two auxiliary cathodes 56, 57 each of which is surrounded by afocusing electrode 58 and 59, respectively. Focusing electrodes 58 and 59 are each respectively provided with a slot 60, 61. The auxiliary cathodes and their focusing electrodes may be mounted adjacent one end of control electrode 43; slot 60 of focusing lectrode 58 opening into the region between grid 43 and main anode 44 and slot 61 of focusing electrode 59 opening into the region between control electrode 43 and main cathode 42. Auxiliary anode 62 is mounted opposite slot 60 across the grid-anode region of the device while auxiliary anode 63 is mounted opposite slot 61 across the grid-cathode region. The grid 43 is arranged to isolate the main cathode 42 from the main anode 44 except for passage through the grid 43. Gas discharge device 55 in operation is similar to device 52 while gas discharge device 55 is somewhat flexible in view of the plural auxiliary circuits. If desired, in operating device 55, auxiliary cathodes 56, 57 may be electrically connected as may also be auxiliary anodes 62, 63. Here again auxiliary anodes 62, 63 may be operated at the potential of main cathode 42.

Still another manner for constructing a gas discharge device for operation at the higher frequencies is shown in FIGURES 6 and 7. The s'pecific construction of gas discharge device 65 is described in detail and claimed in the co-pending joint application of William M. Webster, Edward 0. Johnson and Louis Malter, filed on September 20, 1950, and having Serial No. 185,746, now US. Patent No. 2,588,065, and assigned to th same assignee as the present application. Gas discharge device 65 is provided with a main cathode 66, control electrode or grid 67 and a main anode 68. Main cathode 66 is similar to cathode 13. Grid 67 comprises a plurality of parallel wires 69 supported between insulating members 70, 71 and are joined together by straps 72. Main anode 68 is constructed in a manner similar to grid 67 and comprises a plurality of parallel spaced wires 73 supported between insulating members 70, 71 and interconnected by means of straps '74.

Enclosure members 75, 76 may be made of sheet metal and are spaced as shown so as to substantially enclose main cathode 66, control electrode or grid 67 and anode 68. Enclosure members 75, 76 are conveniently electrically connected to control electrode 67. Adjacent to and closely spaced from each of the open ends of the enclosure members 75, 76 are mounted an auxiliary cathode and focusing electrode which may be similar to those previously described. Auxiliary cathode 77 and focusing electrode 78 is mounted adjacent the cathode end of enclosure members 75, 76 with slot 79 formed in focusing electrode 78 opening toward main cathode 66.

Between slot 79 and main cathode '66 is mounted auxiliary anode 80 comprising a pair of spaced parallel wires 81. Wires 81 are interconnected above insulating member 70 by means of strap 82. Auxiliary anode wires 81 are each located outside of the direct path between slot 79 and main cathode 66.

Similarly auxiliary cathode 83 and focusing electrode 84 are mounted adjacent the main anode end of enclosure members 75, 76 with slot 85 formed in focusing electrode 84 opening toward main anode 68. Auxiliary anode 86, constructed similarly to auxiliary anode 80, is mounted between slot 85 and main anode 68.

The circuit connections for gas discharge device 65 may be similar to those set forth in connection with device 55. Gas discharge device 65 is highly efficient in operation at frequencies of 1.00 megacycles or more.

My invention readily lends itself to other types of devices such as the mixer tube 90, FIGURES 8 and 9. Tube 90 is also a gas discharge device and as in the case of the devices previously described contains an ionizable medium within gas tight envelope 91. Tube 90 comprises a main cathode 92, an auxiliary cathode 93, a focusing electrode 94 which may, as shown, be identical with the corresponding electrodes of gas discharge device 10, Anode 95 corresponds to anode 17 but is rectangular in shape in order to permit the more accurate spacings required in a mixer tube. In device the two control or grid electrodes which are normally present in a mixer tube are interleaved and are mounted in the same plane for reasons which will be pointed out. Alternate wires 96 form one grid and are supported from upper U-shaped collar 97 to which they may b welded. The remaining wires 98 form the other grid and are connected to lower U-shaped collar 99 in a similar manner. The free ends of each of the sets of grid wires extend into holes or recesses formed in upper and lower insulating members 100, 101. Thus, the free ends of grid wires 96 extend into lower insulating member 101 while the free ends of grid wires 98 extend into upper insulating member 100.

The circuit connections for auxiliary cathode 93, focusing electrode 94, main cathode 92 and anode are similar to those previously shown and described for the corresponding elements of gas discharge device 10. Both of the grids may be individually connected across suitable sources of biasing potential to main cathode 92. Connected in series between each of the grids and its source of biasing potential may be a suitable signal source one of which may be the usual local oscillator while the other may be the incoming signal. By interleaving grid wires 96 and 98, the frequency response of device 90 is greatly improved. This is believed to be the case since otherwise time would be required for the plasma to diffuse between the two grids as well as across the space between one of the grids and the anode.

It is not believed necessary to describe the detailed construction of device 90 since as apparent from the drawing, these details are similar to those previously described in connection with the foregoing devices.

From the foregoing, it is apparent that I have provided a gas discharge device which in addition to embodying constructional features not heretofore utilized is also operable so as to-perrnit continuous grid control. I have shown various embodiments of my invention each of which being especially suitable to certain uses as indicated above. Furthermore, gas discharge devices constructed in accordance with my invention have important advan- (cages, for example, the difiicult problem to overcome in gas tubes is that of loss of the gaseous atmosphere to the electrodes and to other structures. This is commonly known as the gas clean-up phenomena. In gas discharge devices constructed in accordance with my invention the voltages and field distribution are such that there tends to be little or no gas clean up in the main conduction circuit. As another example, the low voltages between the main electrodes also eliminates the serious problem of ion bombardment of the main oxide coated cathode. As a result oxide coated cathodes of the usual type may be utilized without their suffering destructive bombardment. Still another important feature is the absence of oscillations in the plasma or noise generally associated with gas discharge devices. In gas discharge devices constructed in accordance with my invention as little as 10 milliamperes or less is all that is required to flow between the ionization or auxiliary electrodes. At this low current level, the objectionable plasma oscillations do not appear and do not interfere with the operation of the device.

It is believed obvious that though I have shown specific embodiments of my invention and described by me in connection therewith, my invention may be applied to gas discharge devices having widely different geometries. Therefore, while my invention is subject to such modifications, it is intended to cover all such modifications which come within the scope of the appended claims.

, What is claimed is:

l. A gas discharge device, comprising a gas tight envelope, an ionizable medium in said envelope, a main thermionic cathode and an anode mounted in spaced relation in said envelope, a control electrode intermediate said main cathode and said anode, at least one ionization cathode in said envelope for creating plasma between said electrode substantially isolating said ionization cathode from said main cathode and said anode, said control electrode extending through said plasma, the diffusion of said plasma being normally free of material interference by said control electrode.

2. A gas discharge device, comprising a gas tight envelope, an ionizable medium in said envelope, a thermionic main cathode, a grid and an anode electrode spaced in that order in said envelope, said grid having at least one open ing formed therethrough which is large compared to the mean free path of an ion of sad medium, an auxiliary cathode spaced from said electrodes for creating a plasma between said main cathode and said anode in said envelope, said plasma normally extending from adjacent said main cathode to adjacent said anode, and a focusing electrode adjacent said auxiliary cathode for focusing the electrons from said auxiliary cathode.

3. A gas discharge device, comprising a gas tight envelope, an ionizable medium in said envelope, main thermionic cathode, grid and anode electrodes spaced in that order in said envelope, said grid having openings formed therethrough which openings are large compared to the mean free path of ions in said medium, an auxiliary cathode in said envelope and spaced from said electrodes, and a cylindrical focusing electrode having a slot formed therethrough and concentric with said auxiliary cathode.

4. A gas discharge device, comprising a gas tight envelope, an ionizable medium in said envelope, main thermionic cathode, grid and anode electrodes spaced in that order in said envelope, said grid having openings formed therethrough which openings are large compared to the mean free path of ions in said medium, an auxiliary cathode in said envelope and spaced from said electrodes, and a cylindrical focusing electrode concentric with said auxiliary cathode, said focusing electrode having a slot formed therethrough opening toward said main cathode.

5. A gas discharge device, comprising a gas tight envelope, an ionizable medium in said envelope, a main thermionic cathode, a U-shaped anode substantially enclosing said main cathode, a U-shaped control electrode spaced from said anode, a cylindrical focusing electrode substantially closing the open end of said U-shaped anode, said focusing electrode having a slot formed therethrough opening toward said main cathode, and an ionization cathode enclosed by said focusing electrode and concentric therewith.

6. A gas discharge device, comprising a gas tight envelope, an ionizable medium insaid envelope, a main thermionic cathode, a U-shapedanode substantially enclosing said main cathode, a U-shaped control electrode spaced from said anode, said control electrode including a plurality of spaced wires, the spaces between said wires being large compared to the mean free path of ions in said medium, a cylindrical focusing electrode substantially closing the open end of said U-shaped anode, and an ionization cathode enclosed by said focusing electrode and concentric therewith, said focusing elect-rode having a slot formed therethrough in alignment with said ionization cathode and said main cathode.

7. A gas discharge device, comprising a gas tight envelope, an ionizable medium in said envelope, an array of electrodes in said envelope including a thermionic cathode, control electrode and an anode mounted in that order, an ionization cathode mounted in said envelope, and a focusing electrode adjacent said ionization cathode and having an aperture formed therethrough opening toward the region between said control electrode and said main anode and said focusing electrode substantially isolating said ionization cathode from said cathode, said control electrode and said anode.

' 8. The method of operating a gas discharge device having a gas tight envelope with an ionizable medium therein having a predetermined ionization potential, an array of load circuit electrodes defining a load current path and including a main thermionic cathode, a control electrode and an anode, an ionization cathode for emitting ionizing electrons for ionizing said medium and forming a plasma which normally extends without interruption between said load circuit electrodes along said path; which comprises impressing a potential between said anode and said main cathode which is less than said ionization potential, impressing a potential between said ionization cathode and said main cathode which is great enough to cause ionization of said medium and the formation of a plasma, and varying the potential between said control electrode and said main cathode to modulate said load current.

9. Gas discharge apparatus, comprising a gas discharge device having a gas tight envelope with an ionizable medium therein having a predetermined ionization potential, an array of load circuit electrodes defining a load current path and including a main thermionic cathode, a control electrode and an anode; means in said envelope for ionizing said medium and creating a plasma; a load impedance having one side thereof connected to said anode, a source of potential less than said ionization potential connected on one side to the other side of said load impedance and on the other side connected to said main cathode, a source of potential greater than said ionization potential and connected on one side to said means and on the other side to one of said electrodes, and a signal source connected between said control electrode and said main cathode.

10. An electron discharge device comprising, an envelope containing a gas, a main thermionic cathode within said envelope for emitting electrons, a hollow main anode surrounding the thermionic cathode for enclosing the space between the main cathode and main anode, a main control electrode mounted adjacent to the inside surface of the main anode, and means for ionizing the space between the main cathode and the main control electrode, said means-including an auxiliary cathode and an auxiliary perforated electrode through which electrons from the auxiliary cathode can pass into the space between the main cathode and the main control electrode.

11'. An electron discharge device comprising, an envelope containing a gas, a main thermionic cathode within said envelope for emitting electrons, a hollow main anode surrounding the thermionic cathode for enclosing the space between the main cathode and main anode, a main control electrode mounted adjacent to the inside surface of themain anode, means for ionizing the space between the main cathode and the main control electrode, said means includingan auxiliary cathode and an auxiliary perforated electrode through which electrons from the auxiliary cathode can pass into the space between the main cathode and the main control electrode, and means for applying a voltage between the auxiliary cathode and the auxiliary perforated electrode for causing electrons to be projected into the space between the main cathode and the main control electrode with sufli'cient energy to ionize the gas therein.

12. A gas discharge device comprising a gas-tight envelope containing an ionizable medium, a group of load current electrodes defining a load current path in said envelope and including thermionic cathode, an anode spaced from said cathode and means including an apertured control electrode interposed between and effectively isolating said cathode and said anode, and auxiliary means for continuously ionizing said medium substantially throughout said load current path from said cathode to said anode independently of the potential difference be tween'said cathode and said anode.

13. A gas discharge device as in claim 12, wherein said auxiliary means comprises a first auxiliary cathode arranged to supply electrons directly to the portion of said load current path between said cathode and said control electrode, and said auxiliary means further includes a second auxiliary cathode arranged to supply electrons directly to the portion of said load current path between said control electrode and said anode.

14. gas discharge device as in claim 13, wherein said auxiliary means further comprises two auxiliary anodes each located on a different side of said control electrode and each opposite one of said auxiliary cathodes.

15. A gas discharge device comprising a gas-tight envelope containing an ionizable medium, a group of load current electrodes defining a load current path in said envelope and including a thermionic cathode, an anode spaced from said cathode and means including an apertured control electrode interposed between said cathode and said anode and effectively isolating said cathode and said anode, and auxiliary means including an auxiliary cathode adjacent to said electrodes and in said envelope for continuously ionizing said medium substantially throughout said load current path from said cathode to said anode independently of the potential difference between said cathode and said anode.

16. A gas discharge device as in claim 15, wherein said auxiliary cathode is arranged to supply electrons directly to the portion of said load current path between said cathode and said control electrode.

17. A gas discharge device as in claim 15, wherein said auxiliary cathode is arranged to supply electrons directly to the portion of said load current path between said control electrode and said anode.

18. A gas discharge device as in claim 15, wherein said auxiliary means further comprises a focusing electrode adjacent to said auxiliary cathode and having apertures therethrough, one of said apertures opening toward the portion of said load current path between said cathode and said control electrode, and one of said apertures opening toward the portion of said load current path be tween said control electrode and said anode.

19. A gas discharge device as in claim 15, wherein said auxiliary means further comprises an auxiliary anode located on the side of said electrodes opposite said auxiliary cathode.

20. A gas discharge device comprising a gas-tight envelope containing an ionizable medium, a group of load current electrodes defining a load current path in said envelope and including a thermionic cathode, an anode spaced from said cathode and means including an apertured control electrode interposed between and effectively isolating said cathode and said anode, and auxiliary means including an auxiliary cathode adjacent to said electrodes and a focusing electrode having an aperture located between said auxiliary cathode and said electrodes for continuously ionizing said medium substantially throughout said load current path independently of the potential difference between said cathode and said anode.

21. The method of operating a gas discharge device having a gas tight envelope with an ionizable medium therein having a predetermined ionization potential, an array of load circuit electrodes defining a load current path and including a main thermionic cathode, a control electrode and an anode, said control electrode dividing said load current path into an anode region and a cathode region, and an ionization cathode for emitting ionizing electrons for ionizing said medium and forming a plasma which normally extends without interruption between said load circuit electrodes along said load current path; which comprises impressing a potential between said anode and said main cathode which is less than said ionization potential, impressing a potential between said ionization cathode and one of said electrodes which is great enough to cause ionization of said medium and the formation of a plasma in both of said regions, and varying the potential between said control electrode and said main cathode to modulate the current in said load current path.

22. A gas discharge device comprising a gas tight envelope, an ionizable medium in said envelope, a thermionic cathode, an apertured control electrode and an anode mounted in spaced relation in said envelope and forming a load current path, said control electrode being interposed between said cathode and said anode and having at least one opening formed therethrough and within said path which is large compared to the mean free path of an ion of said medium, and means in said envelope for creating and maintaining a conductive plasma normally extending substantially from adjacent to said cathode, through said control electrode and to adjacent to said anode during operation of said device.

23. A gas discharge device comprising an envelope; an ionizable medium in said envelope; a cathode and an anode spaced from said cathode and within said envelope and forming a load current path through said envelope; means, including a control electrode interposed between said cathode and said anode, dividing said load current path into two regions; and means for producing and maintaining a conductive plasma in both of said regions and through said control electrode independently of the potential difference applied between said cathode and said anode.

24. A gas discharge device comprising; a sealed envelope containing an ionizable medium, a main cathode and an anode in cooperative spaced relation within said envelope, means including an auxiliary cathode in laterally spaced relation to said main cathode for producing an ionizing discharge to provide a conductive plasma between said main cathode and anode, and means for diverting said ionizing discharge from said main cathode and directing said ionizing discharge into the region between said main cathode and anode.

25. A gas discharge device comprising; a sealed envelope containing an ionizable medium, a main cathode and an anode in cooperative spaced relation within said envelope, means including an auxiliary cathode for producing an ionizing discharge to provide a conductive plasma between said main cathode andanode, and means efiiective for diverting said ionizing discharge from the portion of said main cathode adjacent said auxiliary cathode and directing substantially all of said ionizing dis charge into a portion of the region between said main cathode and anode adjacent said main cathode and substantially spaced from said anode.

26. A gas amplifier tube comprising; a sealed envelope containing an ionizable medium, means for carrying a load current through the tube comprising a main cathode and a main anode in cooperative spaced relationship, means including an auxiliary cathode in laterally spaced relation to said main cathode for producing an ionizing discharge to provide a conductive plasma between said main cathode and anode, means eflective for deflecting said ionizing discharge out of a straight line path between said cathodes, and means effective for directing the deflected portion of said discharge toward the inter-electrode region between said main cathode and anode.

27. A gas-filled current amplifying device comprising: a sealed envelope containing an ionizable medium, a main cathode and an anode in cooperative spaced relation defining an inter-electrode region, means for producing an electron discharge to provide a conductive plasma in said inter-electrode region, and discharge-controlling means effective for causing substantially all of the electrons comprising said discharge to pass through said inter-electrode region before impinging upon any portion of said main cathode and anode, thereby to provide maximum utilization of said discharge in producing plasma in said interelectrode region.

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